Transdermal drug delivery offers many advantages over other types of drug delivery. With transdermal delivery, a localized delivery of drug molecules can be achieved, which makes transdermal drug delivery target specific. Further, transdermal drug delivery avoids the gastro intestinal complications caused by oral delivery. While transdermal drug delivery offers these and other advantages, a system than can quickly and reliably deliver predictable quantities of drug molecules through the skin has heretofore not been developed.
The evolution of transdermal drug delivery has centered around patch technology. Patch technology is based on the ability to hold an active ingredient in constant contact with the epidermis. Over substantial periods of time, drug molecules, held in such a state, will eventually find their way into the bloodstream. Thus, patch technology relies on the ability of the human body to pick up drug molecules through the skin. Transdermal drug delivery using patch technology has recently been applied for delivery of nicotine, in an effort to assist smokers in quitting, the delivery of nitroglycerine to angina sufferers, the delivery of replacement hormones in post menopausal women, etc. These conventional drug delivery systems comprise a patch with an active ingredient such as a drug incorporated therein, the patch also including an adhesive for attachment to the skin so as to place the active ingredient in close proximity to the skin.
Problems with patch technology abound. First, active drug molecules have a difficult time passing through the skin, as the skin poses a significant barrier. In fact, in order for a drug molecule to reach the bloodstream, it must pass through the epidermis, stratum corneum (an especially dense layer of cells), dermis and capillary cell structure. Second, real world conditions such as the patient's obesity, metabolism and circulatory efficiency can effectively prevent transdermal drug delivery from occurring. Third, patch technology can be used only for treatments involving extensively long treatment periods, since the flow rate of drug molecules is so small. Finally, patch adhesion to the skin causes extensive skin trauma as well as cosmetic problems. Specifically, most adhesives currently used tend to aggressively adhere to the skin so that their removal may cause irritation and trauma. Indeed, subsequent patches used by a given individual are often applied to a different area of the skin in order to minimize such irritation and trauma.
In an effort to enhance the efficiency of transdermal drug delivery, the prior art teaches that by mixing certain individual ingredients (penetration enhancers) with a drug molecule, the ability of the drug molecule to pass through the skin is increased somewhat. For example, U.S. Pat. No. 4,933,184 discloses the use of menthol as a penetration enhancer; U.S. Pat. No. 5,229,130 discloses the use of vegetable oil (soybean and/or coconut oil) as a penetration enhancer; and U.S. Pat. No. 4,440,777 discloses the use of eucalyptol as a penetration enhancer.
Although mixing a penetration enhancer with a drug molecule helped to somewhat increase the speed of drug delivery, problems were still present. First, the aforementioned penetration enhancers constitute a passive, not an active, system. Thus, since they were not linked to the drug molecule, the penetration of the enhancer does not necessarily mean that the drug molecule has penetrated. In fact, the prior art drug molecule penetration is only a by-product of the enhancer penetration. Second, even when drug molecule penetration has occurred, the prior art does not establish a condition whereby the blood supply to the transport area is enhanced so as to maximize absorption speed. Third, prior art does not create a molecular structure that releases the drug molecule readily within the acidic medium that constitutes blood, so as to maximize bioavailability of the drug. Finally, although the prior art has increased the speed of transport of the drug molecule transdermally, it is still not sufficiently fast so as to eliminate (if desired) the need for a patch.
It is therefore an object of the present invention to provide a transdermal transport system that efficiently and easily allows for effective delivery of an active ingredient through the skin and into the blood supply of an animal or human.